The present invention is directed to an automated analyzer instrument and, more specifically, is directed to a temperature regulator assembly for an analyzer system such as in chromatography.
For example, in some amino acid analyzers, a very small or micro chromatographic column is used as a specialized application of a liquid column chromatographic separation technique, utilizing ion exchange resin as the stationary phase and eluting buffers of varying pH and salt concentration as the moving phase. Amino acids contained in a sample are introduced at the top of the column and are separated from each other as they are eluted through the resin bed which comprises the column packing. For amino acid analysis, the method of choice for detecting the amino acids in the effluent stream has been to combine the column effluent with a reagent that is metered into the stream at a flow rate proportional to that of the column eluent. When the reagent combines with the amino acids present in the stream, compounds are formed which, when subjected to further development process can be detected by specific changes in optical properties such as absorption or fluorescence.
One of the classical methods in an amino acid analyzer system is that developed by Spackman and Moore, wherein the reagent used in ninhydrin dissolved in a suitable solvent/buffer solution. Under this process, the column effluent/reagent solution is heated in a reactor to a fixed temperature for a specified period of time. The compounds developed as a result of this process will have specific colors, the intensities of which are proportional to the amounts of compounds contained in the flowing stream. The optical densities of these compounds are measured at specific wavelengths. For any of these systems in which stream blending is utilized as part of a detection process, it is important that the operating temperature of the column be very stable. In other words, short-term variations in temperature must be negligible. This is due to the fact that the thermal coefficients of the column and its packing material cause the internal void areas in the column to vary with temperature. In a constant flow system the column which is inserted between the buffer source and the stream blending tee becomes a variable element whose volume is temperature dependent. Variations in temperature are then translated into variations in flow rate of a column effluent. This, in turn, affects the stream blending ratio, which appears as a fluctuation in the analyzer base line.
For use in a micro column amino acid analyzer, this basic system can be automated to analyze samples which are automatically injected into the chromatographic column in a cyclic or repetitive manner wherein the physical conditions of temperature and flow rate are repeated with close precision. The temperature of the chromatographic column is critical to the exchange rate of ions between the liquid phase and the resin bed. Column temperature must be maintained or varied in precisely determined patterns in order to obtain calibration repeatability in an automated amino acid analyzer. Generally, during an analytical procedure, the temperature is increased from a starting level to an elevated end value in a predetermined manner. In automatic analysis it is important that the temperature be returned to stable initial conditions as rapidly as possible in order to minimize the recycle time of the instrument. Under some conditions it is necessary for the starting column temperature to be lower than ambient which requires that the column be cooled. Consequently, it is important that a temperature regulating system for use on the chromatographic column be capable of not only precisely controlling the temperature during the analysis, but also regulating the temperature as rapidly as possible over a wide range of values.
In most prior systems, the temperature of the chromatographic column has been regulated by utilizing some type of liquid bath surrounding the column wherein the temperature of the bath is controlled which in turn controls the column temperature. In this type of system, the thermal inertia of the water makes it relatively easy to limit the previously mentioned short-term cyclic temperature variations. However, this type of system does not provide the requisite speed in regulating the temperature of the column. The use of some type of liquid bath around the column requires additional plumbing and space for the system which is not only more expensive, but also can lead to additional maintenance problems. In addition, the use of a liquid or water jacket surrounding the column to thermostat the temperature can require a considerable amount of power to obtain a relatively slow heating rate. A typical system can require as much as 750 watts to obtain a heating rate of 1.degree. C. per minute. The operation of a liquid bath is such that the rapid cooling from the elevated temperature is provided by immersing a coil within the bath through which cold water is circulated as required.
Another approach which has been used for controlling the temperature of a column is to attach the column to some type of thermally conductive block having electrical resistance heating elements. The cooling required is provided by blowing ambient air across the block. The problem with these arrangements is that their operation is limited to temperatures above ambient.